Metal/silicon contact and methods of fabrication thereof

ABSTRACT

Methods and resulting structures for thermally stable metal/silicon contacts are described. The resulting contacts are aluminum which is alloyed with at least one noble metal from the group of Pd and Pt wherein at least one region of the contact is further alloyed with silicon.

TECHNICAL FIELD

The present invention relates in general to metal/silicon ohmic contactsand Schottky barrier contacts, and particularly to an improved aluminumsilicon ohmic or Schottky barrier contact with enhanced thermalstability.

BACKGROUND ART

It has been appreciated that an aluminum-silicon interaction occurs whenaluminum is in direct contact with silicon at elevated temperatures. W.Chu et al in IBM Technical Disclosure Bulletin, Volume 19, No. 7, p.2532 (December 1976), suggest employing a transition metal oxide as anintermediate layer between the aluminum contact and the silicon toovercome this problem. While the Chu et al technique eliminatesinteraction of aluminum with silicon, a high resistance contact mayresult due to the existence of the interface between the transitionmetal oxide and the silicon.

An alternative solution to the use of transition metal oxides as areaction barrier has been to interpose silicides and/or metallic layersbetween the underlying silicon and the conductor metallurgy.

When a silicide is interposed between an aluminum conductor and asilicon substrate, then, depending on the impurity concentration in thesilicon either an ohmic or Schottky barrier contact as well as areaction barrier is formed between the aluminum and the silicon.However, the aluminum conductor may react with the silicide duringsubsequent elevated temperature processing steps such as annealing, andresult in penetration of the aluminum through the silicide. This canresult in alteration of the electrical characteristic of the originalsilicide-silicon contact, e.g. in a Schottky barrier and it may resultin electrically shorting the height of the underlying junction. Thisproblem has been addressed by Hollins in U.S. Pat. No. 3,906,540 and issolved by using an intermediate layer of a refractory metal, such as Mo,Ti, W, Ta, or alloys thereof, to block the interaction of the aluminumwith the silicide. The use of Cr as the intermediate layer between analuminum contact and a silicide was pointed out by T. M. Reith and M.Revitz in IBM Technical Disclosure Bulletin, Vol. 16, No. 11, page 3586(April 1974). Since the silicide is usually formed by depositing a metalonto the silicon substrate, and thereafter heating to react and form asilicide, the problem of a high resistance interface does not existbetween the silicide and the silicon substrate. Instead a highlyresistive interface can exist between the refractory metal and thesilicide because of the nature of such an interface, and also, becauseof possible contamination of the silicide refractory metal interface. Inaddition, generation of this hierarchy of metallic film composites canlead to unwanted stress phenomena, embrittlement, or delamination whichimpairs the reliability of the contact.

P. S. Ho et al in the IBM Technical Disclosure Bulletin, Vol. 21, No. 8,page 3372, January 1979, have extended the principle of using anintermediate layer between an aluminum contact and the silicide layer.Their technique substitutes either aluminum-palladium oraluminum-platinum alloys for the refractory metals. These alloys serve afunction similar to that served by the refractory metal by providing abarrier to prevent the interaction of the aluminum with the silicide.

The methods of Ho et al, Reith et al, and Hollins, all require asilicide to be formed on a silicon substrate before their method can bepracticed. As has been mentioned earlier, the silicide is usually formedby depositing a metal onto the silicon substrate and thereafter heatingto react with the silicon substrate to form a silicide. Thus, ingeneral, the formation of the silicide, such as PtSi and Pd₂ Si, resultsin consumption of an amount of silicon from the substrate about equal tothe amount of metal deposited thereon. In the case of shallow junctionswhich are to be contacted such as those in small insulated gate fieldeffect transistors (FET's), the consumption of silicon in forming auseable contact can result in depletion of a significant portion, of theactive region of the device making the design of a practical processwhich takes into account process tolerances very difficult. Whenextremely shallow junctions are to be contacted there may be nopractical process.

Alternatively, Rosvold in U.S. Pat. No. 3,938,243 teaches theco-deposition of Pt and Ni onto a silicon substrate and thereafterreacting to form a ternary alloy with silicon. The resulting ternaryalloys which he describes are mixtures of about equal amounts of Pt-Niand silicon. These alloys will interact with an aluminum conductor in afashion similar to the reaction of other silicides unless methods suchas those of Ho et al, Reith et al, or Hollins are employed to preventsuch interaction. Furthermore, formation of such ternary silicidesconsume silicon in an amount similar to what occurs during the formationof PtSi for Pd₂ Si making these ternary alloys marginally useful forshallow junctions.

Crowder et al in a copending application, Ser. No. 811,914 assigned tothe assignee of the present application, discloses a method forcodepositing a silicide onto a silicon substrate by co-evaporation ofsilicon and a silicide forming metal. While this technique eliminatesthe problems of the consumption of silicon from the substrate it doesnot offer an opportunity for reaction of the deposited silicide with thesubstrate. Since the deposited layer does not react with the substrate,a high resistance interface is probably created between the substrateand the deposited material, thereby limiting its effectiveness as acontact

Furthermore, this technique does not address the problem of theAl-silicide penetration phenomenon, and further processing steps, suchas those suggested by Ho et al, and Hollins, will be required toovercome this problem.

The use of an intermetallic compound as a reaction barrier has beenproposed by Magdo in U.S. Pat. No. 3,995,301 assigned to the presentassignee. This patent teaches depositing aluminum onto a silicide layer,thereafter heat treating in a temperature range of 400° or 450° totransform the silicide to form an aluminum-platinum compound of the formof Al₂ Pt. This technique provides a new contact of Al₂ Pt to thesilicon substrate which lowers the barrier height from about 0.8 eV ofPtSi to about 0.72 eV. The Magdo patent requires the deposition of asilicide forming metal onto the silicon substrate and reactingthereafter to form a silicide. Since a silicide layer must be formedduring processing this technique will be subject to the same limitationsas earlier set forth with respect to the formation of a silicide barriercontact on shallow junction devices. Using a similar approach, andHoward et al in U.S. Pat. No. 4,140,020 discloses and claims theformation of binary intermetallic compounds on the surfaces of siliconsubstrates used for contacts and Schottky barriers. In this lattertechnique, metals forming binary intermetallic compounds are codepositedand subsequently reacted by heat treating. Again, this technique suffersfrom the same shortcoming as does the method of Crowder et al in thatthere will be no reaction between the silicon substrate and the layersdeposited thereon which is necessary to avoid formation of a highresistance interface.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an illustration of a prior art Schottky barrier contact withan associated aluminum connector.

FIG. 2 is an illustration of one embodiment of the contact of thepresent invention with an associated aluminum conductor.

FIG. 3 is a flow diagram illustrating fabrication steps for theproduction of the prior art device of FIG. 1.

FIG. 4 is a flow diagram illustrating the fabrication steps for oneembodiment of the method for producing the contact of the presentinvention.

FIG. 5 is a flow diagram illustrating the fabrication steps for a secondembodiment of the method for producing the contact of the presentinvention.

FIG. 6 is an illustration of the test sample configuration for I-V testmeasurements.

DISCLOSURE OF INVENTION

It is an object of this invention to provide an insitu formed ohmicmetal contact for heavily doped silicon substrates.

A second object of this invention is to provide an insitu formedSchottky barrier between a metal contact and a silicon substrate.

A third object of this invention is to provide a method for fabricationof thermally stable ohmic contacts which contain a ternary compound.

A further object of this invention is to provide a method for forming acontact which reacts with the silicon substrate on heat treatment, butin which the reaction with the substrate consumes only small quantitiesof the silicon thereby allowing fabrication of thermally stable shallowjunctions.

Still another object of this invention is to provide a junction which isthermally stable to temperatures as high as approximately 500° C. in thepresence of an overlying aluminum film.

These and other objects of this invention will become more apparent fromthe study of the device herein described and the method for fabricationof the same.

The contact comprises aluminum alloyed with a noble metal from the groupof Pd or Pt. At least a region of the contact adjacent to the substrateis further alloyed with Silicon.

The contact is fabricated by co-depositing an alloy of aluminum and atleast one noble metal from the group of Pt and Pd onto a siliconsubstrate. The aluminum content of the co-deposited layer is betweenabout 40 to 60 atomic %. The co-deposited alloy is heated to betweenabout 400° C. to 600° C. for a time sufficient to develop a region atthe substrate interface which is further alloyed with silicon.

BEST MODE OF CARRYING OUT THE INVENTION

FIG. 1 is a representation of a prior art metal/silicon ohmic contactdeposited on a p-n silicon junction. The silicon substrate 10 is joinedto an aluminum conductor 12 through a series of intermediatemetallurgies. Typically, a platinum or palladium silicide layer 14 willbe in contact with the silicon substrate 10 to form the ohmic contact tothe junction. Then, interposed between the silicide layer 14 and theconnector 12 will be a barrier layer 16. This barrier layer may be arefractory metal, such as chromium or alternatively an aluminumpalladium or aluminum platinum compound. The resulting contactfrequently is susceptible to excessive resistance due to the nature ofthe interface between the silicide layer 14 and the barrier layer 16,and possible contaminations at the surface 18 which forms the interface.Another problem with the prior art contacting procedure is that theformation of the silicide layer 14 consumes silicon from the substrate10. For Pd₂ Si and PtSi, the Si consumption, as measured by the depth ofsilicide penetration d, will be about equal to the thickness of themetal layer which was deposited on the substrate 10 and thereafterreacted with it to form a silicide. In the case of devices with ashallow n⁺ active region 19 such as insulated gate field effecttransistors, IGFET's, it is possible for the consumption of the n⁺active region 19 by the silicide layer 14 to destroy the characteristicsof the resulting device during formation of the contact. An even moreserious problem is that during annealing treatments following conductormetallization and patterning the conductor metal may penetrate throuughthe silicide and through the junction destroying the latter if anadditional barrier layer is not present. In IGFET fabrication suchadditional barrier layers are not normally employed and therefore thejunctions are particularly subject to penetration of the conductormetal.

FIG. 2 is a pictorial representation of one embodiment of the presentinvention. A silicon substrate 10 is attached to an aluminum conductor12 through an intermediate layer 14' which is an alloy of aluminum andone of the noble metals, either Pd or Pt. At least a region of the layer14' is further alloyed with silicon to form an aluminum noble metalsilicon alloy. When Pd is employed the preferred alloy is Al₃ Pd₄ Si,and when the noble metal employed is platinum the preferred ternaryalloy is Al₃ Pt₄ Si. In contrast to the formation of the prior artbinary alloy Pd₂ Si or PtSi, the ternary alloy, Al₃ Pd₄ Si or Al₃ Pt₄Si, consumes only about 1/7 of the amount of silicon. This results inreduced penetration depths d' for equivalent metal deposits and thisleaves the n⁺ active region 19 substantially intact, avoidingdegradation of the characteristics of the resulting device. The ternaryalloy region is generated at the interface 18' between the siliconsubstrate 10 and the noble metal aluminum alloy region 14. It ispreferable that as much of the region 14 be alloyed with silicon as ispractical thereby forming an aluminum noble metal silicon compoundthroughout the region 14.

In fabricating a device such as represented in FIG. 1 or FIG 2, asilicon substrate of the n type silicon having a doping level of about10¹⁶ atoms per cc can be utilized to form a Schottky barrier junction,otherwise a more heavily doped n or p type substrate can be used to forman ohmic contact. The selection of appropriate doping levels to form anohmic contact or a Schottky barrier contact is well recognized in theart.

FIG. 3 is a flow diagram which characterizes the steps typicallyundertaken to produce the prior art structure such as shown in FIG. 1.After cleaning, the silicon substrate 10 is placed in a chamber and thepressure is reduced to approximately 10⁻⁷ torr, and thereafter Pt or Pdis deposited onto the silicon substrate 10 as is indicated in step 32.The deposit thickness is typically about 500 A.

After deposition, the substrate 10 is sintered in vacuum for about 20minutes. In the case of a palladium deposit the temperature forsintering is approximately 250° C., while for a platinum deposit thetemperature is about 600° C. The sintering treatment is illustrated instep 34 and converts the deposited metal to a silicide layer 14 shown inFIG. 1.

Optionally, to assure the removal of any residual platinum or palladiummetal, the substrate 10 with the attached silicide layer 14 may beremoved from vacuum and etched to remove any residual unreacted metal.Palladium may be removed by employing potassium iodide as an etchant,while platinum may be removed with aqua regia. This optional step isshown in the FIG. 3 by step 36 which is shown with a broken line toindicate that it is optional.

Subsequent to the sintering step 34 an optional second deposition step38 may be employed where a metal layer, such as Cr or Al and either Ptor Pd is deposited onto the silicide layer 14. This deposit forms thebarrier layer 16 as illustrated in FIG. 1. The barrier layer 16 isdeposited in a vacuum and its thickness is approximately 500 A. If thisstep is omitted as is the current practice in IGFET devices penetrationof the conductor metal may occur during subsequent processing.

Finally, the aluminum conductor metallurgy 12 as illustrated in FIG. 1,is evaporated onto the barrier layer 16. Before the final deposition ofthe conductor. It is possible to use intermediate masking steps (notshown) to assure the proper patterning, of alternatively, the patterningmay be effected after the aluminum is deposited.

The flow diagram of FIG. 3 illustrates the processing steps andmetallization techniques which can be employed to produce the prior artdevice illustrated in FIG. 1. The process requires depositing twointermediate metallic layers between the contact and the substrate. Thenecessity for deposition of two metallic layers has been eliminated bythe present invention. Furthermore, the reaction of the noble metal withthe substrate 10 to form a noble metal silicide layer 14, such as Pd₂ Sior PtSi, requires a consumption of Si, the volume of which is aboutequal to the volume of metal deposited in step 32. This reaction resultsin significant penetration of the silicide layer 14 into the siliconsubstrate 10 which creates a problem in designing a practical processfor contacting very shallow junctions such as exist in μm or smallerFET's. This consumption problem can be eliminated by the presentinvention since the formation of the Al-noble metal silicide consumesonly about 1/7 the volume of Si required by the noble metal silicide inthe prior art device.

In addition, the method of the present invention reduces the number ofprocess steps required to form a reliable contact. FIG. 4 is a flowdiagram for one method of practicing the present invention. Thesubstrate is placed in an evacuated chamber after suitable preparationand the chamber is evacuated to about 10⁻⁷ torr and preferably belowthat pressure. Thereafter, an alloy of aluminum and at least one noblemetal from the group of platinum and palladium is deposited onto thesubstrate. The aluminum content of the codeposited layer is betweenabout 40 to 60 atomic %. When the aluminum content is maintained withinthese compositional limits and only one noble metal is employed it hasbeen found that upon appropriate heat treatment as subsequentlydescribed, a silicide of the form of Al₃ Pd₄ Si or Al₃ Pt₄ Si will form.It is preferable that the co-deposited alloy be about 50 percentaluminum to assure a more complete formation of such a ternary compound.The co-deposition may be accomplished by a variety of techniques suchas:

(a) simultaneous evaporation of aluminum and the noble metal fromindividual sources using two electron beam power supplies,

(b) sputtering from a homogeneous alloy target of the appropriatecomposition, or

(c) simultaneous evaporation using resistive heating of two sources.

Typically, these co-deposited layers should be between about 200 A and1500 A thick.

Subsequent to the deposition of the co-deposited aluminum noble metalalloy the aluminum metallurgy 12 shown in FIG. 2 may be deposited.Typically, the thickness of the aluminum contact is between about 1/4micron and 1 micron.

The co-deposition of the aluminum alloy and the deposition of thealuminum metallurgy can be accomplished in a single step as isillustrated in step 42 of FIG. 4. In this case, during the early part ofthe deposition, a controlled quantity of noble metal is co-depositedwith aluminum and thereafter only the aluminum is deposited. If forexample an AlPd layer is desired, it can be obtained by employing anevaporation rate for aluminum of about 6 A/sec and for Pd of about 5A/sec. After correcting for the density difference, this combination ofthe evaporation rates gives about equal atomic compositions for Al andPd. The evaporation can be carried out at room temperature under avacuum of about 10⁻⁶ to 10⁻⁷ torr.

After the deposition step has been completed the composite structure isheated. During the heat treatment step 44, the substrate and depositedlayer are heated to between about 400° C. to approximately 600° C. for atime sufficient to form a region which is further alloyed with silicon.It is preferred to heat for a time sufficient, to completely react theco-deposited aluminum noble metal layer with silicon. For a 1000 A alloyfilm these times will be typically 1/2 hour. Al₃ Pd₄ Si is formed whenthe co-deposited noble metal is Pd.

A co-deposited Al and Pt layer forms a silicide compound which has anelectron diffraction pattern observed using a transmission electronmicroscope to be virtually identical to that of Al₃ Pd₄ Si. The compoundof Al₃ Pt₄ Si has not been reported in the published literature, butbased on the diffraction pattern the compound has been tentativelyidentified as Al₃ Pt₄ Si.

A systematic series of tests were conducted to establish the parameterswhich controlled the formation of ternary silicides. The test resultsare summarized in Table I and illustrate the structure which is observedfrom co-evaporation of 800 A to 1500 A of a noble metal aluminum alloyonto a SI substrate and subsequent heat treatment. From a thermodynamicpoint of view one would expect that the ternary compounds would co-existwith binary compounds or a binary compound and the pure elementdepending upon the Al-noble metal ratio deposited and thetime-temperature treatment applied in the essentially nonequilibriumprocess used.

These binary phases and any aluminum phase which are formed duringreaction is located on top of the reacted junction of Al₃ Pd₄ Si/Si orAl₃ Pt₄ Si/Si. Defraction studies indicate both the AlPd and Al₂ Pt havea cubic crystal structure.

                                      TABLE I                                     __________________________________________________________________________    Deposition     PHASES PRESENT AFTER HOLDING                                   Rates A/Sec.   AT ANNEALING TEMPERATURE FOR 1/2 HOUR                          Al                                                                              Pt or Pd                                                                           Deposited Film                                                                        300° C.                                                                          400° C.                                                                        500° C.                                                                     600° C.                          __________________________________________________________________________    7 4    Al.sub.0.6 Pd.sub.0.4                                                                 Al.sub.3 Pd.sub.4 Si                                                                    Al.sub.3 Pd.sub.4 Si                                                                  Al.sub.3 Pd.sub.4 Si                                                               Al.sub.3 Pd.sub.4 Si                           (1800A) +         +       +    +                                                      AlPd (˜20%)                                                                       Al      Al   Al                                                     +                                                                             Al                                                             6 5    Al.sub.0.5 Pd.sub.0.5                                                                 AlPd      Al.sub.3 PdSi                                                                         Al.sub.3 Pd.sub.4 Si                                                               Al.sub.3 Pd.sub.4 Si                           (1800A) + Al.sub.3 Pd.sub.4 Si (<5%)                                                            + AlPd  + AlPd                                                                             + AlPd                                                 + small amount                                                                          (top layer)                                                         Pd.sub.2 Si                                                    5 2      Al.sub.0.75 Pd.sub.0.25                                                             AlPd      AlPd    AlPd AlPd                                           (1800A) +         +       +    +                                                      Al        Al      Al   Al                                      5 5    Al.sub. 0.5 Pt.sub.0.5                                                                Al.sub.2 Pd                                                                             Al.sub.3 Pt.sub.4 Si (30%)                                                            Al.sub.3 Pt.sub.4 Si                                                               Al.sub.3 Pt.sub.4 Si                           (500A)  +         +       +    +                                                      Pt        Al.sub.2 Pt                                                                           Al   Al                                                               + Pt                                                 __________________________________________________________________________

As can be seen from examination of this table, in order to obtain thedesired ternary alloy compounds it is necessary to limit theconcentration of the aluminum in the co-evaporated deposits. In general,the ratio aluminum to noble metal should be kept in the atomic ratio ofbetween 3 to 2 and 2 to 3. It should be noted, that when the ratio of Alto Pd becomes 3 to 1 the desired ternary alloy does not occur.

Furthermore, to establish substantial transformation to the ternaryalloy it can be seen from examination of Table I that it is preferred toanneal the co-deposited metal at a temperature between about 400° C. and600° C.

It should be appreciated that the heat treatment which promotes reactionof the silicon with the co-deposited metal will reduce contactresistance and overcome the problem resulting from techniques such asthose suggested by Crowder et al where no reaction occurs between thedeposited layer and the Si substrate. Furthermore, although the presentinvention promotes reaction between the silicon substrate theconsumption of Si is minimized. When the aluminum noble metal alloy iswithin the compositional ranges specified by the present invention theappropriate temperature for heat treatment will be between about 400° C.to about 600° C. The alloy formed requires consumption of relativelylittle silicon since it is either Al₃ Pd₄ Si or Al₃ Pt₄ Si. Theconcentration of silicon in these alloys is much lower than that for thecomparable binary silicides, PtSi or Pd₂ Si.

When masking steps are required to produce the metallization for thecontacts, additional steps will be required as is illustrated by theflow diagram in FIG. 5. In this case, the first step is theco-deposition of an aluminum noble metal alloy as is illustrated in step52. Thereafter, the co-deposited alloy will be heat treated as discussedabove, step 54. After the heat treatment, masking steps may beimplemented to effect the final patterning during the deposition step 56to form the aluminum contact.

In order to aid in accessing the characteristics of the contacts of thepresent invention, a series of samples were prepared for I-Vmeasurements. The geometry of the I-V test device is illustrated in FIG.6. Silicon doped with n type impurities to yield a resistance of about 1to 10 Ω-cm is employed as a substrate 60. A SiO₂ layer 62 having a roundaperture 64, is deposited onto the substrate 60. The diameter of theaperture 64 is either 1, 4, 9 or 16 mils. A layer of co-depositedaluminum noble metal alloy 66 approximately 1500 A thick is depositedinto the aperture 64 and contacts the substrate 60. The alloy upon heattreatment forms the desired ternary alloy. In contact with theco-deposited alloy 64 is an Al contact 18 about 1500 A in thickness.

A variable voltage supply 70 is electrically connected to the contact 68and the substrate 60.

An I-V analysis of the Schottky barrier junction forward biascharacteristics can be made by varying the potential applied andrecording the resulting current. A semilogarithmic plot of the currentvs. the voltage yields a straight line. The slope of the line isproportional to the inverse of the ideality index and the zero currentintercept of the line can be used to calculate the Schottky barrierheight.

Further details of the test procedure for metal semiconductor rectifiersare found in the article by V. L. Rideout "A Review of the Theory,Technology and Application of Metal--Semiconductor Rectifiers", ThinSolid Films, Vol. 48, pp. 261-291 (1968).

The results of the tests are tabulated in Table II.

Good thermal stability was observed for the tested barrier junctionunder sequential annealing up to 500° C. judging from the relativelyconstant values of the barrier height and the ideality index. Inaddition, the small values of the standard deviations indicate goodreproductibility of the test device characteristics.

                  TABLE II                                                        ______________________________________                                        RESULTS FROM I-V MEASUREMENTS ON                                              SCHOTTKY BARRIER JUNCTIONS                                                                        NO. OF   BARRIER IDEAL-                                                       SAM-     HEIGHTS ITY                                      SAMPLE   HEAT       PLES     IN eV.  INDEX n                                  STRUC-   TREAT-     MEAS-         Std.      Std.                              TURE     MENT       URED     Av.  dev. Av.  dev.                              ______________________________________                                        Al/AlPd/Si                                                                             As-deposited                                                                             10       0.80 0.01 1.06 0.02                                       400° C. 1/2 hr.                                                                   12       0.81 0.02 1.06 0.03                                       450° C. 1/2 hr.                                                                   12       0.77 0.02 1.07 0.01                                       500° C. 1/2 hr.                                                                   11       0.73 0.01 1.07 0.01                              Al/Al.sub.3 Pd.sub.2 /Si                                                               As-deposited                                                                             11       0.83 0.01 1.04 0.02                                       400 ° C. 1/2 hr.                                                                   9       0.83 0.01 1.04 0.02                                       450° C. 1/2 hr.                                                                    8       0.83 0.01 1.05 0.02                                       500° C. 1/2 hr.                                                                    7       0.83 0.01 1.03 0.01                              Al/AlPt/Si                                                                             As-deposited                                                                             18       0.70 0.02 1.08 0.01                                       400° C. 1/2 hr.                                                                    9       0.72 0.01 1.07 0.05                                       500° C. 1/2 hr.                                                                   11       0.72 0.01 1.05 0.01                              ______________________________________                                    

As can be seen from analyzing the results tabulated in Table II, thetest samples provide for barriers which are not subject to thermaldegradation. These structures are stable when the temperature of heattreatment is between about 450° C. and 550° C. and the Al to noble ratiofalls within the ranges earlier set forth. Furthermore, the idealityindex of the samples, which is an index of the merit of the Schottkybarrier, approaches the value of unity. For an ideal Schottky barrierthis value would be unity.

The fact that these materials are stable when so heat treated allowsgreater flexibility in the process steps which can be employed infabricating devices employing the contact of the present invention.

Industrial Applicability

The present invention is well suited to the semiconductor industry foruse in fabricating ohmic and/or Schottky barrier contacts. Thefabrication technique herein described is generally useable forfabrication of semiconductor devices and is particularly useful forfabrication of shallow junction devices such as those employed ininsulated gate field effect transistors (IGFET's).

While the novel features of the invention have been described in termsof preferred embodiments and for particular industrial applications, itwill be understood that various omissions and substitutions in the formand details of the method and device illustrated or other applicationsmay be made by those skilled in the art without departing from thespirit of the invention.

Having thus described our invention, what we claim as new, and desire tosecure by Letters Patent is:
 1. A contact for making an electricalconnection between an aluminum conductor and a silicon substratecomprising:aluminum alloyed with at least one noble metal from the groupPd and Pt to form a resultant alloy wherein at least one region of saidresultant alloy is further alloyed with silicon; and wherein the ratioof Al to said noble metals is in the atomic ratio of between about 3 to2 and 2 to
 3. 2. The contact of claim 1, wherein said further alloyedregion has the ratio of Si to other elements of between about 1 to 6 and1 to
 10. 3. The contact of claim 2, wherein said noble metal is Pt andsaid further alloyed region forms the compound Al₃ Pt₄ Si.
 4. Thecontact of claim 2, wherein said noble metal is Pd and one said furtheralloyed region forms the compound Al₃ Pd₄ Si.
 5. The contact of claim 1,wherein said region alloyed with Si is throughout said contact.